This invention relates to evaporation cooling systems for internal combustion engines.
German Patent 3,339,717 discloses an evaporation cooling system in which an individual heating circuit having a circulation pump and a heat exchanger is connected to the cooling chambers of the engine to heat the passenger compartment of a motor vehicle equipped with the engine. Since a condensate pump is as a general rule also required in the condensate line of the engine cooling circuit, this separation of vehicle heating and engine cooling circuits involves considerable expense, especially in terms of the separate pumps. Also, since only a portion of the coolant circulates through the vehicle heater, the effectiveness of the heater is limited when the engine is operating with little exhaust heat, as generally occurs in high-efficiency engines.
On the other hand, the above-described evaporation cooling system is advantageous because it is a closed system, so that escape of the coolant to the atmosphere is avoided, thus maintaining the quality of the coolant and protecting the environment. Also, the fact that the evaporation cooling system or its components are only partially filled with liquid coolant when the engine is cold permits consistent application of the principle of evaporation cooling. Thus, at least one compensation tank with a bladder providing an elastically yielding wall is included to accommodate air displaced by the evaporated coolant, but not the coolant itself.
This advantage of complete separation of the coolant-filled chambers and lines from the environment is not provided by the evaporation cooling systems disclosed in U.S. Pat. No. 4,367,699. Those systems include air and vent lines which open, by way of valves if required, to the atmosphere rather than opening into compensation tanks which are sealed off from the environment. If a heat exchanger for a vehicle heater is provided, it is included in the vapor line extending between the engine and the condenser, and consequently it becomes effective only after evaporation of the coolant. To expedite warm-up of the cold engine, an additional warm-up circuit for liquid coolant having a electric pump controlled by the liquid coolant temperature is connected directly to the cooling chambers of the engine. Hence the devices disclosed in that patent involve a considerable expense requiring, for example, still another pump in the warm-up circuit in addition to the pump in the condensate line.
A more elegant solution is described in German Offenlegungsschrift No. 38 09 136. Here again, there is a system for evaporation cooling, and when the engine is warm, a heating circuit for a vehicle heater containing a coolant pump and a heat exchanger forms an auxiliary condenser, branching off the main condenser. In this known system, which requires a large volume of coolant because the several components are completely flooded, the heat exchanger thus receives both liquid and vaporized coolant. In this arrangement, however, the provision of a small capacity heating circuit and a large capacity cooling circuit requires a switching system and appropriate controls.